With the popularization and development of digital cameras, pixel counts have increased. Meanwhile, attempts are being made to find methods enabling more faithful color reproduction. A color management system is available as a method enabling more faithful color reproduction. A color management system is a system with which identical colors can be reproduced between different devices. By employing image data conforming to the sRGB standard, for example, during image data exchange between different devices, color reproduction that is less device-dependent can be realized.
In addition to reductions in device-dependency during color reproduction, attempts are being made to widen the gamut. For example, Adobe RGB and so on are known as standards enabling color reproduction in a wider gamut.
However, when an attempt is made to achieve more faithful color reproduction by further increasing color reproducibility, there is a limit to the color reproduction that can be achieved using three primary colors such as B (blue), G (green) and R (red). Therefore, methods enabling color reproduction in a wider gamut, such as methods for handling images using a larger number of primary colors than three, for example 6, 8, 16, and so on, are being developed.
In this specification, a method employing more than three primary colors will be referred to as a multi primary color method, and likewise a method employing a larger number of bands than three will be referred to as a multiband method.
JP3826174B discloses an image capturing apparatus capable of generating multi primary color image data. In the image capturing apparatus disclosed in JP3826174B, light emanating from an imaging lens is divided into two beams by a half mirror. One of the beams is led to a luminance detection imaging device to obtain the luminance of an object, while the other beam is further divided by a dichroic mirror and then led to a shorter wavelength component imaging device and a longer wavelength component imaging device. Spectral information relating to the object is estimated on the basis of color signals output by the short wavelength component imaging device and the long wavelength component imaging device. The estimated spectral information of the object is then applied to a lightness signal obtained from the luminance detection imaging device, whereby an eight-color multiband image is generated.
Further, “Comparison of spectral image reconstruction methods using multipoint spectral measurements”, MURAKAMI Yuri and 3 others, Color Forum JAPAN, 2007 Proceedings, Meeting of Managers of Four Academic Associations Concerning Optics, November 2007, p. 133-136 discloses a method enabling generation of more faithful images, albeit RGB three primary color images, which uses a three band camera employing a BGR three primary color imaging device and a multipoint spectral measurement sensor attached to the three band camera to be capable of measuring a spectrum in a plurality of locations on an object.
In this technique, the spectral sensor scans the object from the upper, lower, left and right such that the spectrum of the object is measured at a plurality of measurement points, i.e. 8×8, 16×16, 32×32, 64×64. A spectral reflectance image is then generated through estimation from three band image data output by the three band camera and the object spectrum measurement result obtained by the multipoint spectral measurement sensor. An XYZ image is then determined as an image simulating the appearance of the colors of the object when the spectral reflectance image is illuminated by illumination light having an arbitrary spectral radiance. A display RGB image is then generated by applying a display characteristic of a display device to the XYZ image.
According to the technique disclosed in the paper written by Murakami et al, an image having a reduced color difference can be obtained by increasing the number of measurement points during spectral measurement using a multipoint spectral measurement sensor.